Problem: Let N be a positive odd number.

There are N coins, numbered 1, 2, \ldots, N. For each i (1 \leq i \leq N), when Coin i is tossed, it comes up heads with probability p_i and tails with probability 1 - p_i.

Taro has tossed all the N coins. Find the probability of having more heads than tails.

Constraints

* N is an odd number.
* 1 \leq N \leq 2999
* p_i is a real number and has two decimal places.
* 0 < p_i < 1

Input

Input is given from Standard Input in the following format:


N
p_1 p_2 \ldots p_N


Output

Print the probability of having more heads than tails. The output is considered correct when the absolute error is not greater than 10^{-9}.

Examples

Input

3
0.30 0.60 0.80


Output

0.612


Input

1
0.50


Output

0.5


Input

5
0.42 0.01 0.42 0.99 0.42


Output

0.3821815872

Solution (in PYTHON3):

Solution:
# coding: utf-8
# Your code here!
N=int(input())
P=list(map(float,input().split()))

dp=[[0]*(N+1) for i in range(N+1)]

dp[0][0]=1
for n in range(N):
    for i in range(n+1):
        j=n-i
        dp[j][i+1]+=dp[j][i]*P[n]
        dp[j+1][i]+=dp[j][i]*(1-P[n])

ans=0
for i in range((N+1)//2):
    ans+=dp[i][-i-1]

print(ans)